Preparation, characterization and gas sensitivity of polypyrrole/γ-Fe2O3 hybrid materials

Polypyrrole (PPy)/γ-Fe2O3 hybrid materials were prepared by sol–gel polymerization in situ and characterized by Fourier transform infrared (FT-IR), X-ray powder diffraction (XRD), thermogravimetric and differential thermal analysis (TG–DTA) and high-resolution transmission electron microscope (HRTEM). The gas sensitivities in CO, H2, NH3, ethanol or acetone atmospheres were determined at 30 °C, 60 °C and 90 °C. FT-IR and XRD patterns suggest that ferric oxide in the hybrids was γ-Fe2O3, with a diameter of approximately 5 nm. TG–DTA and HRTEM analyses showed that different reactant molar ratios of pyrrole monomer: Fe(NO3)3·9H2O resulted in different microstructures of γ-Fe2O3 and molecular weights of PPy. An increased amount of Fe(NO3)3·9H2O increased the degree of uniformity of the molecular weight of PPy and resulted in a change of γ-Fe2O3 microstructure from granular to stick particles. The results of gas sensitivities showed that the PPy/γ-Fe2O3 hybrids exhibited high sensitivity to NH3 at mild operating temperature (<100 °C). Furthermore, the sensing mechanism was also discussed.